Abstract
Microtubule arrays are prominent molecular machineries managing proper regulations of cell number and shape. Spatial and temporal controls of microtubule arrays are essential for regular development. To understand the molecular mechanism of microtubule organization, we have analyzed function of a plant-specific kinesin-like protein, API1, which is expressed in dividing cells of the moss Physcomitrella patens.
Disruption of API1 or its sister gene, API1L alone did not result in any noteworthy phenotype, but double disruption of API1 and API1L caused formation of incomplete cell plate and multinucleated cells, and reduced and misoriented polar growth. In the double disruptants, the spindle was distorted and the midline of the phragmoplast was unusually expanded. The API1-GFP and API1L-YFP fusion proteins were localized in the equatorial plane of spindles and phragmoplasts, where the plus ends of microtubules overlap. Thus these proteins may crosslink antiparallel microtubules at the equatorial plane of spindles and phragmoplasts.
